Since laminated glass generates only a small amount of scattering glass fragments even when subjected to external impact and broken, laminated glass is excellent in safety. As such, the laminated glass is widely used for automobiles, railway vehicles, aircraft, ships, buildings and the like. The laminated glass is produced by sandwiching an interlayer film for laminated glass between two glass plates.
Examples of the interlayer film for laminated glass include a single-layered interlayer film having a one-layer structure and a multi-layered interlayer film having a two or more-layer structure.
As an example of the interlayer film for laminated glass, the following Patent Document 1 discloses a sound insulating layer including 100 parts by weight of a polyvinyl acetal resin with an acetalization degree of 60 to 85% by mole, 0.001 to 1.0 part by weight of at least one kind of metal salt among an alkali metal salt and an alkaline earth metal salt, and a plasticizer in an amount greater than 30 parts by weight. This sound insulating layer can be used alone as a single-layered interlayer film.
Furthermore, the following Patent Document 1 also describes a multi-layered interlayer film in which the sound insulating layer and another layer are layered. Another layer to be layered with the sound insulating layer includes 100 parts by weight of a polyvinyl acetal resin with an acetalization degree of 60 to 85% by mole, 0.001 to 1.0 part by weight of at least one kind of metal salt among an alkali metal salt and an alkaline earth metal salt, and a plasticizer in an amount of 30 parts by weight or less.
The following Patent Document 2 discloses an interlayer film which is constituted of a polymer layer having a glass transition temperature of 33° C. or more.
The following Patent Document 3 discloses a polyvinyl acetal-based resin film having a thickness distribution in the width direction of 10% or less and a volatile matter content of 1.0% by mass or less. In this polyvinyl acetal-based resin film, when two 5%-inside portions from both ends in the width direction of the film overall width are heated for 30 minutes at 150° C. respectively, a value of the thermal shrinkage ratio of one 5%-inside portion larger in thermal shrinkage ratio in the flow direction, which is parallel to the film and perpendicular to the width direction is defined as the thermal shrinkage ratio MD1, a value of the thermal shrinkage ratio of the other 5%-inside portion smaller in thermal shrinkage ratio therein is defined as the thermal shrinkage ratio MD2, and a value of the thermal shrinkage ratio of a central portion in the flow direction, which is parallel to the film and perpendicular to the width direction, obtained at the time of heating the central portion in the width direction of the film for 30 minutes at 150° C. is defined as the thermal shrinkage ratio MD3, all of the thermal shrinkage ratio MD1, the thermal shrinkage ratio MD2 and the thermal shrinkage ratio MD3 are 3 to 20%.